Validating Age Estimates from Pectoral Fin Spines and Length-Frequency Analysis of Known-Age Shortnose Sturgeon

The pectoral fin spine is the most accepted hard structure used for estimating ages of sturgeons. However, sturgeon age validation studies indicate that age estimation using fin spines typically underestimate sturgeon ages, particularly of older fish. Underestimating the ages of these long-lived species can result in inaccurate findings in population dynamics studies, such as overestimation of growth and mortality parameters. The shortnose sturgeon (Acipenser brevirostrum) is a long-lived, critically endangered fish for which population declines are attributed to anthropogenic effects. One method for evaluating recovery of shortnose sturgeon is through assessments of recruitment and population age structure, which are evaluated via age estimation with pectoral spines and modal assignments from length frequency (L-F) histograms. However, the accuracy of these estimation techniques is unknown, and inaccuracies could hinder conservation decision-making. Therefore, we collected pectoral fin spines from known and unknown age shortnose sturgeon in the Savannah, Ogeechee, and Altamaha Rivers, Georgia, from 2004–2023 to assess accuracy of age estimation procedures. Both the coefficient of variation and average percent error calculated from between-reader age estimates derived from pectoral fin spines were low. Mean consensus age estimates from known-age fin spines typically overestimated ages of younger fish and underestimated ages of fish older than 5 years. Age estimates from fin spines and back-calculated length-at-age estimates both supported the age-1 assignment from a length-frequency histogram. However, age assignments from pectoral fin spines suggest multiple ages present in the age-2+ size bin, indicating that age assignments from length-frequency histograms alone would lead to inaccuracies in demographic-based analyses.